For transmitting a speech or audio signal in a packet communication system represented by an Internet communication or a mobile communication system and/or the like, compression/encoding techniques are widely used to improve transmission efficiency of the speech or audio signal. Furthermore, in recent years, although speech or audio signals are simply encoded at a low bit rate, there is a growing demand for a technique for encoding a wider band speech/audio signal.
In response to such a demand, various techniques for encoding a wide band speech or audio signal without drastically increasing the amount of encoded information are being developed. According to a technique disclosed in Patent Literature 1, and/or the like, an encoding apparatus calculates parameters to generate a spectrum of a high-frequency portion of a frequency of spectral data obtained by converting input acoustic signals corresponding to a certain time and outputs the parameters together with encoded information of a low-frequency portion. More specifically, the encoding apparatus divides the spectral data of the high-frequency portion of the frequency into a plurality of subbands and calculates in each subband, a parameter that identifies a spectrum of the low-frequency portion most approximate to the spectrum of the subband. Next, the encoding apparatus adjusts the spectrum of the most approximate low-frequency portion using two types of scaling factors so that the peak amplitude in the high-frequency spectrum generated or energy of the subband (hereinafter, referred to as “subband energy”) and the shape thereof become close to the peak amplitude, subband energy and shape of the spectrum of the high-frequency portion of a target input signal.